CBE Doctoral Dissertation Defense: “MEMS-Based Electrochemical Power Sources for Extended Operational Duration of Micro Unmanned Vehicles” (Yanghang Huang)

Abstract:

Micro unmanned vehicles, defined as 25-gram to 5-kg in weight, are increasingly being utilized in applications such as search and rescue or agricultural monitoring. Such vehicles are typically powered with lithium-ion batteries. However, vehicle operational efficiency and capability are often compromised by the limited energy density of these batteries, resulting in short operational duration. This dissertation explores high-energy chemistries beyond lithium-ion batteries, including metal-air batteries and fuel cells, as power sources to significantly extend the operational duration of both the kilogram-scale and gram-scale micro unmanned vehicles.

Three different power source chemistries are proposed and investigated for different types of micro unmanned vehicles: gram-scale micro unmanned-ground-vehicles; gram-scale micro unmanned-aerial-vehicles; and kilogram-scale micro unmanned-aerial-vehicles.

1. Gram-Scale Unmanned-Ground-Vehicles: Micro zinc-air batteries are developed for extended operation durations for gram-scale unmanned-ground-vehicles. The lean electrolyte operation of the battery enhances its gravimetric performance; however, this approach suffers from rapid electrolyte degradation, limiting battery performance. The study identifies carbonation and slow zincate decomposition as the main degradation mechanisms. Based on these findings, a discharge energy model is developed, successfully predicting the discharge performance of the micro zinc-air battery. Insights from the degradation study are used to enhance the electrochemical performance of micro zinc-air batteries, demonstrating their potential to significantly extend the operation duration of gram-scale unmanned ground vehicles.

2. Gram-Scale Micro Unmanned-Aerial-Vehicles: Due to the higher power requirements of gram-scale unmanned aerial vehicles, micro aluminum-air batteries are developed as onboard power sources. The cell design and cell packaging of the battery are optimized to achieve an energy density of 320 Wh/kg above a power density of 500 W/kg, far surpassing the performance of equivalent commercial lithium-ion batteries. A 3D-printed small-scale quadrotor platform is used to evaluate flight duration, with the micro aluminum-air battery delivering 13.1 minutes of flight time compared to the 4.5 minutes of the commercial micro lithium-ion battery. This demonstration also marks the first successful untethered flight of a gram-scale micro unmanned-aerial-vehicle powered by air batteries. Additionally, cathode fabrication techniques are explored, utilizing a Ag-based cathode developed through microfabrication techniques to maximize the electrochemically active surface area. This cathode can support the necessary power density for the small-scale quadrotor while offering a potential cost reduction of 1/1500th of that of conventional cathodes. This work highlights the potential of micro aluminum-air batteries to serve as efficient, cost-effective, and long-lasting power sources for gram-scale unmanned-aerial-vehicles.

3. Kilogram-Scale Micro Unmanned-Aerial-Vehicles: For kilogram-scale micro unmanned-aerial-vehicles, solid oxide fuel cells are investigated. A flight duration model is first developed, showing that the solid oxide fuel cell is promising for significantly extending the flight duration. To meet the power requirement of the kilogram-scale micro unmanned-aerial-vehicle, a microfabrication process for thin-film solid oxide fuel cells is developed, aiming to increase its power performance. While preliminary results confirm the successful fabrication of the thin-film cell, scaling the technology to power the kilogram-scale micro unmanned-aerial-vehicle remains a significant challenge.

This work demonstrates that high-energy-density electrochemical power sources with simultaneous high-power-density for micro unmanned vehicles are feasible. Such unconventional high-energy power sources, including zinc-air batteries, aluminum-air batteries, and solid oxide fuel cells, show significant potential to substantially extend operational durations of multiple micro unmanned vehicle types.